Gas separation device and method of use

ABSTRACT

A gas separation device for separating oxygen gas from air includes a compressor; a concentrator; a measurement mechanism; and a flow control mechanism that includes a valve assembly for providing fluid flow control, the valve assembly having a motor; a valve body; and a plunger within the valve body and reciprocally driven by the motor, wherein the valve body including a fluid inlet, a fluid outlet, and a flow chamber therebetween, the flow chamber including a flow chamber wall and a flow chamber outlet, the plunger including a flexible member reciprocating within the flow chamber outlet to provide variable flow control therethrough, the flexible member including a lip seal engageable with the flow chamber wall during reciprocation of the plunger and flexible member to provide a seal therebetween.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application is a continuation of U.S. patent application Ser. No.10/835,700, filed on Apr. 30, 2004, now U.S. Pat. No. 7,025,329, whichis incorporated by reference herein as though set forth in full.

FIELD OF THE INVENTION

The field of this invention relates, in general, to valves for controlof fluid flow and, in particular, to a valve for control of product flowin oxygen concentrators.

BACKGROUND OF THE INVENTION

Oxygen concentrators are commonly used in the home medical market totreat patients with chronic obstructive pulmonary diseases. Due to thewide availability of these oxygen concentrators on the market, themarket for these devices is highly cost competitive and is expected tobecome even more competitive in the future. In order to remaincompetitive in this market, it is critical to reduce the manufacturingcost associated with every component in the oxygen concentrator system.The flow measurement and control system is one aspect of the overallconcentrator system that may be cost-reduced; however, a less expensiveflow system will only be viable if it provides sufficient accuracy andreliability.

Commercially available oxygen concentrators generally use one of twotechnologies to control the flow of product gas. The most common is arotameter (flowmeter with a floating ball) combined with a manuallycontrolled needle valve. Rotameters may be inexpensive, but in order tomaintain accuracy, they are often coupled with a pressure regulator.Even combined with the regulator, due to pressure variations downstreamof the rotameter, these needle valve/rotameter combinations provide anaccuracy of about 10% which is sufficient for most home medical oxygenconcentrators. Nonetheless, once combined with a regulator, this controlmethod would not be considered inexpensive.

Another common technology is the use of an orifice plate in combinationwith a pressure regulator. The orifice plate usually contains 10 or moreprecision orifices, each providing an exact flow when an exact pressureis provided on the feed side. The regulator is used to provide a fixedpressure on the feed side. The orifice plate/regulator combinationfunctions by allowing the user to adjust a dial to a specific orifice inorder to provide a specific product flow. This method of flow control isgenerally more accurate than a rotameter; however, it is also moreexpensive and is also subject to inaccuracy due to downstream pressurefluctuations.

A need clearly exists for a low-cost, accurate flow control system foran oxygen concentrator. One method of achieving this goal makes use ofthe increasingly common use of acoustic systems to measure oxygenconcentration in oxygen concentrators. For negligible additional cost,these acoustic systems can be modified to measure oxygen flow inaddition to concentration. Coupling the flow measurement with aninexpensive motorized valve would result in a low-cost, accurate flowcontrol system.

SUMMARY OF THE INVENTION

To solve these problems and others, an aspect of present inventionrelates to a method of providing fluid flow control in a needle valveassembly. The method includes providing a needle valve assemblycomprising a motor, an internally threaded valve body, and an externallythreaded plunger threadably engaged with the internally threaded valvebody and rotatably and reciprocally driven by the motor, the valve bodyincluding a fluid inlet, a fluid outlet, and a flow chambertherebetween, the flow chamber including a flow chamber wall and a flowchamber outlet, the plunger including a flexible needle member thatreciprocates within the flow chamber outlet to provide variable flowcontrol therethrough, the flexible needle member including a lip sealthat engages the flow chamber wall during reciprocation of the plungerand flexible needle member to provide a seal therebetween; supplyingfluid flow to the fluid inlet of the needle valve assembly; providingvariable flow control in the needle valve assembly through reciprocationof the flexible needle member in the flow chamber outlet; and sealingyengaging the flow chamber wall with the lip seal of the flexible needlemember to prevent fluid flow therebeween.

A further aspect of the invention involves a needle valve assembly forproviding fluid flow control. The needle valve assembly includes amotor; an internally threaded valve body; and an externally threadedplunger threadably engaged with the internally threaded valve body androtatably and reciprocally driven by the motor, wherein the valve bodyincluding a fluid inlet, a fluid outlet, and a flow chambertherebetween, the flow chamber including a flow chamber wall and a flowchamber outlet, the plunger including a flexible needle memberreciprocating within the flow chamber outlet to provide variable flowcontrol therethrough, the flexible needle member including a lip sealengageable with the flow chamber wall during reciprocation of theplunger and flexible needle member to provide a seal therebetween.

A further aspect of the invention relates to the flexible, elastomericnature of the flexible needle member of the valve. The flexiblecharacteristics of the material reduces the amount of torque required toseal the valve compared to the prior art and the amount of precisionrequired in the valve components in order to insure a complete seal.

A further aspect of the invention involves the capability to adjust flowunder varying downstream pressure effects. The invention coupled withcontrol and measurement electronics enables the device to keep the flowat the set-point value regardless of upstream or downstream pressureeffects.

A further aspect of the invention is the small number of parts requiredfor the needle valve assembly. Fewer parts leads to the lowmanufacturing cost of the valve which is critical for the application.

Further objects and advantages will be apparent to those skilled in theart after a review of the drawings and the detailed description of thepreferred embodiments set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simple schematic of an embodiment of a gas separationdevice.

FIG. 2 is a perspective view of an embodiment of a needle valveassembly.

FIG. 3 is a partial cross-sectional view of the needle valve assembly ofFIG. 2.

FIG. 4 is an enlarged cross-sectional view of a portion of the needlevalve assembly of FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to FIG. 1, a gas separation device 10 constructed inaccordance with an embodiment of the invention will first be describedbefore describing an embodiment of a needle valve assembly 100. The gasseparation device 10 may include a compressor 20, a Pressure SwingAdsorption (PSA) Module or concentrator 30, a measurement mechanism 40,and a flow control mechanism 50. In use, a feed fluid such as ambientair may be drawn into the compressor 20 and delivered under highpressure to the PSA Module 30. The PSA module 30 separates a desiredproduct fluid (e.g., oxygen) from the feed fluid (e.g., air) and expelsexhaust fluid. Characteristics of the product fluid (e.g., flow/purity)may be measured by a measurement mechanism 40. Delivery of the productfluid may be controlled with the flow control mechanism 50.

With reference to FIGS. 2-4, an embodiment of a needle valve assembly100 that is ideal for use in a flow control mechanism 50 of a gasseparation device 10 will now be described. The needle valve assembly100 includes a one-piece valve body 120 and a motor 130. The motor 130includes a motor mount 140 for mounting the motor 130 to motor mountbosses 150 of the valve body 120. Threaded fasteners (not shown) may beused to secure the motor mount 140 to the motor mount bosses 150. Thevalve body 120 may include additional mounting bosses 160 for mountingthe needle valve assembly 100 to another component of the gas separationdevice 10. Power and control may be supplied to the motor 130 through anelectrical connector 170. A motor gear 180 (FIG. 3) is carried on amotor shaft 190. The motor 130 is a stepper motor that rotates the motorshaft 190 and the motor gear 180 in a clockwise or counter-clockwisemanner. In the embodiment shown, the motor 130 is a 48 step/rev steppermotor that provides roughly ¼ Liter per minute flow resolution with afeed pressure of 10 psig. In other embodiments, the motor 130 may havemore or less than 48 steps/rev to provide either finer resolution withmore steps/rev or faster response with less steps/rev.

A geared screw 200 of a reciprocating and rotating plunger 210 isoperatively engaged with the motor gear 180. In the embodiment shown,the gear ratio of the geared screw 200 to the motor gear 180 is 4:1. Thegear ratio affects the torque and resolution of the needle valveassembly 100. In an alternative embodiment, motor 130 could operate as adirect drive without motor gear 180 when the torque is sufficientlysmall. In another alternative embodiment, the gear ratio of the gearedscrew 200 to the motor gear 180 could be as high as necessary (e.g.,100:1) to provide the increased resolution and higher torque that mightbe required in large systems. The rotating plunger 210 includes aplunger shaft 212 with external threads 214 that are threadingly engagedwith internal threads 216 of the valve body 120 and a bore 218. Anelastomeric, flexible, one-piece needle member 220 includes a shaft 230received within the bore 218, and a head 240. In the preferredembodiment, the shaft 230 and bore 218 have non-circular (e.g., square)cross sections such that when the rotating plunger 210 is rotated, theflexible needle member 220 will also rotate. The head 240 of the needlemember 220 includes a tip portion 250 and an integral lip seal 260. Inan alternative embodiment, the lip seal 260 may be a separate elementfrom the needle member 220.

With reference to FIGS. 3 and 4, the valve body 120 includes an inlet270 having an inlet passage 280, an outlet 290 having an outlet passage300, and a flow chamber 310 including flow chamber wall 312. The tippotion 250 of the needle member 220 is disposed in the flow chamber 310.Near an interface of the outlet passage 300 and the flow chamber 310,the valve body 120 includes a flow chamber outlet port 320. Outletpassage walls 330 terminate at one end at the outlet port 320.

With reference to FIGS. 2-4, the needle valve assembly 100 will now bedescribed in use. The motor 130 rotates the motor shaft 190 in aclockwise or counter-clockwise manner, causing motor gear 180 to rotatein a opposite manner. Rotation of motor gear 180 causes geared screw 200and externally threaded plunger 210 to rotate. Rotation of theexternally threaded plunger 210 within internally threaded valve body120 causes the plunger 210 and, hence, the elastomeric needle member220, to reciprocate within the valve body 120, depending on thedirection of rotation of the motor 130. Movement of the top portion intoand out of the flow chamber outlet port 320 creates a variable orificein the needle valve assembly 100. Increased movement of the elastomericneedle member 220 towards the flow chamber outlet port 320 causes thetip portion 250 to further block the flow chamber outlet port 320,further inhibiting or stopping fluid flow through the inlet passage 280,flow chamber 310, and outlet passage 300. The flexible, elastomericnature of the needle member 220 allows the tip portion 250 to flex andseal against the outlet passage walls 330 as the needle member 220 ismoved towards the flow chamber outlet port 320. The flexible,elastomeric needle member 220 relaxes concentricity requirements andminimizes the required torque by the motor 130 to reduce or stop flowthrough the needle valve assembly 100. Increased movement of theelastomeric needle member 220 away from the flow chamber outlet port 320causes the tip portion 250 to further withdraw and increase the openingat the flow chamber outlet port 320, further increasing fluid flowthrough the inlet passage 280, flow chamber 310, and outlet passage 300.Pressure on the lip seal 260 and the needle member 220 keeps the tipportion 250 engaged. Thus, by controlling reciprocating movement of theneedle member 220, fluid flow through the needle valve assembly 100 iscontrolled. While the elastomeric needle member 220 reciprocates in thevalve body 120, the flexible, elastomeric lip seal 260 sealingly engagesthe flow chamber walls 312, preventing the escape of fluid flow throughthis part of the valve body 120. This lip seal 260 is integrally formedwith the elastomeric, one-piece needle member 220. As mentioned above,in an alternative embodiment, the lip seal 260 may be separate from theelastomeric needle member 220. The lip seal 260 eliminates the need fora gasket or o-ring for sealing within the valve body 120. The lip seal260 additionally allows the volume of the flow chamber 310 to beminimized, further reducing the size of the needle valve assembly 100.Relative to other types of gaskets, the lip seal 260, and specificallythe small size and the small diameter of the lip seal 260, functions tolower the torque required by the motor 130 to operate the needle valveassembly 100. Use of integrated lip seal 260 eliminates the need for ano-ring or an external lip seal, which add additional complexity in thedesign. Thus, the main advantages to the lip seal 260 are reduced costthrough a reduced number of parts and reduced torque required by themotor.

Utilizing a 48 step/rev stepper motor and a gear ratio of 4:1 for thegeared screw 200 and the motor gear 180 provides about 120 steps betweenthe closed and the full-flow positions. In alternative embodiments, alarger or smaller number of steps could be specified to provide eithermore precision or faster adjustment. Because resolution of the flowcontrol in the needle valve assembly 100 is a function of the motor 130and the gear ratio, the pressure differential resolution can beincreased or decreased in the needle valve assembly 100 by adjustingthese two variables. Utilizing a higher gear ratio between the gearedscrew 200 and the motor gear 180 allows a smaller motor 130 to be usedand allows for precise movement of the needle member 220 for precisefluid flow control and improved flow control accuracy of less than about¼ Liter per minute at 10 psig. However, this accuracy could be adjustedby changing the gear ratio and the stepper motor.

In an alternative embodiment, the head 240 of the elastomeric needlemember 220, the flow chamber 310, and the outlet passage 300 may belonger and narrower, or shorter and wider than that shown in FIGS. 1-3to allow increased or decreased resolution of the flow control.

The needle valve assembly 100 consists of three main parts: 1) thestepper motor 130, 2) the internally threaded valve body 120, and 3) theexternally threaded plunger 210 with needle member 220. This simpleconstruction of the needle valve assembly 100 allows the needle valveassembly 100 to be smaller, have less parts, be more precise (whencoupled with closed-loop control electronics), and less expensive tomanufacture than needle valve assemblies in the past, making the needlevalve assembly 100 an economic means to provide flow control in a flowcontrol mechanism 50 of a gas separation device 10.

It will be readily apparent to those skilled in the art that stillfurther changes and modifications in the actual concepts describedherein can readily be made without departing from the spirit and scopeof the invention as defined by the following claims.

1. A method of providing fluid flow control in a gas separation devicefor separating oxygen gas from air, comprising: providing a gasseparation device for separating oxygen gas from air, the gas separationdevice including a flow control mechanism with a valve assembly, theneed valve assembly including a motor, a valve body, a plunger in thevalve body reciprocally driven by the motor, the valve body including afluid inlet, a fluid outlet, and a flow chamber therebetween, the flowchamber including a flow chamber wall and a flow chamber outlet, theplunger including a flexible member that reciprocates within the flowchamber outlet to provide variable flow control therethrough, theflexible member including a lip seal that engages the flow chamber wallduring reciprocation of the plunger and flexible member to provide aseal therebetween; separating oxygen gas from air using the gasseparation device and controlling product flow in a flow controlmechanism using the valve assembly by: supplying fluid flow to the fluidinlet of the valve assembly; providing variable flow control in thevalve assembly through reciprocation of the flexible member in the flowchamber outlet; sealably engaging the flow chamber wall with the lipseal of the flexible member to prevent fluid flow therebeween.
 2. Themethod of claim 1, wherein the flexible member is a one-piece memberwith the lip seal integrally formed therein.
 3. The method of claim 1,wherein the motor is a stepper motor including at least 24steps/revolution.
 4. The method of claim 1, wherein the motor and theplunger include respective gears and the gear ratio of the gear of theplunger to the gear of the motor is at least 1:1.
 5. The method of claim1, wherein the motor is a stepper motor, and the motor and the plungerinclude respective gears.
 6. The method of claim 1, wherein the valveassembly is a needle valve assembly and the flexible member is aflexible needle member.
 7. A gas separation device for separating oxygengas from air, comprising: a compressor that receives ambient air; aconcentrator that receives the air under high pressure from thecompressor; separates oxygen from air, and delivers oxygen as a productfluid; a measurement mechanism that measures characteristics of theproduct fluid; a flow control mechanism that controls delivery of theproduct fluid, the flow control mechanism including: a valve assemblyfor providing fluid flow control, comprising: a motor; a valve body; anda plunger within the valve body and reciprocally driven by the motor,wherein the valve body including a fluid inlet, a fluid outlet, and aflow chamber therebetween, the flow chamber including a flow chamberwall and a flow chamber outlet, the plunger including a flexible memberreciprocating within the flow chamber outlet to provide variable flowcontrol therethrough, the flexible member including a lip sealengageable with the flow chamber wall during reciprocation of theplunger and flexible member to provide a seal therebetween.
 8. The valveassembly of claim 7, wherein the flexible member is a one-piece memberwith the lip seal integrally formed therein.
 9. The valve assembly ofclaim 7, wherein the motor is a stepper motor including at least 24steps/revolution.
 10. The valve assembly of claim 7, wherein the motorand the plunger include respective gears and the gear ratio of the gearof the plunger to the gear of the motor is at least 1:1.
 11. The valveassembly of claim 7, wherein the motor is a stepper motor, and the motorand the plunger include respective gears.
 12. The needle valve assemblyof claim 7, wherein the valve assembly is a needle valve assembly andthe flexible member is a flexible needle member.